A method for catalyzing the oxidation esterification of ethylene glycol to methyl glycolate using a palladium-based nanolaminate catalyst

Abstract

The application discloses a method for preparing methyl glycolate by catalyzing ethylene glycol oxidative esterification through a palladium-based nano-alloy catalyst, and belongs to the technical field of catalysis. The palladium-based nano-alloy catalyst takes the noble metal palladium as a main active component, takes an oxide or a composite oxide as a carrier, and simultaneously adds at least one of bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese and magnesium as an auxiliary agent to adjust the catalyst. The palladium-based nano-alloy catalyst is prepared through an impregnation method, a deposition precipitation method or a coprecipitation method, the reaction activity and product selectivity are remarkably improved in the reaction of catalyzing ethylene glycol oxidative esterification to prepare methyl glycolate, the efficient conversion from ethylene glycol to methyl glycolate is realized, and the method has a very wide industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalysis technology, and particularly relates to a method for preparing methyl glycolate by catalyzing ethylene glycol oxidative esterification with a palladium-based nano-alloy catalyst. BACKGROUND

[0002] Methyl glycolate (HOCH2COOCH3) has both alcohol and ester chemical properties due to the presence of alpha-H, hydroxyl and ester functional groups, and can undergo carbonylation, amination, hydrolysis, hydrogenation and oxidative dehydrogenation and other chemical reactions, and is widely used in various fields such as chemical industry, pesticides, medicines, feed additives, dyes and the like. In addition, methyl glycolate is also a good solvent for cellulose, resin and rubber, etc.

[0003] The methods for synthesizing methyl glycolate mainly include: addition of formaldehyde and hydrocyanic acid, radical addition of methyl acetal and formaldehyde, carbon-based esterification of formaldehyde, and coupling reaction of methyl formate and formaldehyde, etc. Due to the high price of raw materials, the serious corrosion in the production process, and the difficulty in separating the product, these processes have been gradually eliminated.

[0004] Qin Xiaoxia et al. used Au / ZnO to selectively oxidize and catalyze ethylene glycol to synthesize methyl glycolate, and found that the Au / ZnO catalyst with a gold loading mass fraction of 5% had the best catalytic performance in the reaction of synthesizing methyl glycolate by ethylene glycol oxidative esterification (the eighth national industrial catalysis technology and application annual meeting, 2011, conference papers). Although gold-based catalysts show excellent activity, the price of gold is relatively high. In order to reduce the cost, palladium catalysts can be a good choice. However, compared with gold catalysts under the same reaction conditions, the selectivity of palladium-based catalysts for catalyzing methyl glycolate is lower. Therefore, it is an urgent technical problem to be solved to improve the palladium-based catalysts and then improve the activity and selectivity of the palladium-based catalysts for catalyzing methyl glycolate. SUMMARY

[0005] In order to solve the problems in the background art, the present application aims to provide a method for preparing methyl glycolate by catalytic oxidation esterification of ethylene glycol using a palladium-based nano-alloy catalyst. The palladium nano-particles are loaded on an oxide or composite oxide carrier by an impregnation method or a deposition precipitation method to prepare a supported palladium catalyst. By introducing elements such as bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium for doping (catalyst modification mechanism: by introducing elements such as bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium for doping, forming an alloy or intermetallic compound with palladium, adjusting the coordination environment of palladium, thereby adjusting the electronic properties of palladium, weakening the adsorption strength of palladium on organic reactants and the dissociation ability of C-C bond, reducing the production of by-products, and improving the conversion rate of ethylene glycol and the selectivity to the product), the catalyst is reduced and used in the reaction of preparing methyl glycolate by catalytic oxidation esterification of ethylene glycol, thereby significantly improving the oxidation esterification activity of ethylene glycol and the selectivity to the product.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions.

[0007] The present application provides a method for preparing methyl glycolate by catalytic oxidation esterification of ethylene glycol using a palladium-based nano-alloy catalyst, which comprises the following steps:

[0008] (1) The soluble salt of the modified metal is impregnated on the oxide or composite oxide carrier, and is left to stand at room temperature for 10-24 hours. After drying, the modified oxide or composite oxide carrier is calcined in an air atmosphere at 400-700 DEG C. The palladium salt solution is impregnated on the surface of the modified oxide or composite oxide carrier in an equal volume. Alternatively, the palladium salt aqueous solution is mixed with the modified oxide or composite oxide carrier, and then an alkali solution is added to adjust the pH to 8-13. After being left to stand at room temperature for 2-24 hours, the mixture is dried and calcined in an air atmosphere at 400-700 DEG C. Finally, the catalyst is reduced in a hydrogen atmosphere at 150-500 DEG C.

[0009] Alternatively, the palladium salt solution and the soluble salt of the modified metal are impregnated on the oxide or composite oxide carrier together. After being left to stand at room temperature for 10-24 hours, the mixture is dried and calcined in an air atmosphere at 400-700 DEG C. Finally, the catalyst is reduced in a hydrogen atmosphere at 150-500 DEG C.

[0010] (2) The catalyst obtained in step (1) is loaded into a high-pressure reaction kettle, and a mixed solution of an alkaline substance, ethylene glycol, and methanol is added. The reaction is carried out in an oxygen-containing atmosphere. The reaction pressure is 0.5-5 MPa, and the reaction temperature is 80-200 DEG C. Ethylene glycol is oxidized and esterified to obtain methyl glycolate.

[0011] Based on the above technical solution, further, the modified metal mentioned in step (1) is one or more of bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium, and the loading of the modified metal is 0.1-2wt%, preferably 0.5-1.5wt%.

[0012] Based on the above technical solution, further, the palladium metal loading in step (1) is 0.1-5wt%, preferably 0.5-1.5wt%.

[0013] Based on the above technical solution, further, the palladium salt mentioned in step (1) is one of palladium sulfate, nitrate, oxalate, chloride, acetate, and phosphate.

[0014] Based on the above technical solution, further, the soluble salt of the modified metal mentioned in step (1) is the sulfate, nitrate, oxalate, chloride, acetate, or phosphate of the corresponding metal.

[0015] Based on the above technical solution, further, the oxide mentioned in step (1) is one of Al2O3, MgO, SiO2, CaO, ZnO, TiO2, and ZrO2, and the composite oxide is a mixture of two of Al2O3, MgO, SiO2, CaO, ZnO, TiO2, and ZrO2, with a mass ratio of the two oxides of 10:1 to 1:10.

[0016] Based on the above technical solution, further, the solute of the alkaline solution in step (1) is one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonia, and urea.

[0017] Based on the above technical solution, further, the drying in step (1) is carried out at 100-140℃, the calcination temperature is 400-600℃, the calcination time is 2-6h, the reduction temperature is 300-500℃, and the reduction time is 1-5h.

[0018] Based on the above technical solution, further, in step (2), the reaction pressure is 1-3 MPa, the reaction temperature is 100-130℃, and the reaction time is 0.5-24h.

[0019] Based on the above technical solution, further, the alkaline substance mentioned in step (2) is sodium hydroxide, potassium hydroxide, sodium carbonate, or potassium carbonate, and the concentration of the alkaline substance is 0.0001-0.1 g / mL.

[0020] Based on the above technical solution, further, in step (2), the molar ratio of methanol to ethylene glycol is 0.1-50:1, preferably 5-50:1; the amount of catalyst added is 0.1-20wt% of the total amount of methanol and ethylene glycol, preferably 1-10wt%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] To reduce catalyst costs while improving the selectivity of methyl glycolate, this invention loads relatively inexpensive palladium nanoparticles onto an oxide or composite oxide support. By adding a second element such as bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, or magnesium, the activity of the catalyst and the selectivity of the product are modulated. This allows for an activity close to that of gold salts at 120-150°C, which is more conducive to industrial production applications. Attached Figure Description

[0023] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0024] Figure 1 This is a TEM image of the palladium-bismuth nanoalloy catalyst from Example 1.

[0025] Figure 2 SEM image and elemental distribution diagram of the palladium-bismuth nanoalloy catalyst in Example 1; Detailed Implementation

[0026] The present invention will be described in detail below through specific embodiments, but these embodiments do not constitute a limitation on the content of the present invention.

[0027] The reaction products were analyzed online by gas chromatography.

[0028] The conversion rate of ethylene glycol is calculated as follows:

[0029] Conv(ethylene glycol)% = [1 - (amount of unreacted ethylene glycol / amount of supplied ethylene glycol)] × 100%

[0030] The selectivity of methyl glycolate is calculated as follows:

[0031] S(methyl glycolate)% = [Amount of methyl glycolate produced / (Amount of ethylene glycol supplied - Amount of unreacted ethylene glycol)] × 100%.

[0032] Comparative Example 1: Preparation of 1% Pd / Al2O3

[0033] 0.2 mL of chloropalladic acid aqueous solution was added dropwise to the Al2O3 support to achieve a palladium loading of 1%. After impregnation, the mixture was allowed to stand at room temperature for 12 h, then dried at 120 °C for 2 h, calcined at 500 °C in air for 2 h, and finally reduced at 400 °C in hydrogen atmosphere for 2 h to obtain the catalyst 1% Pd / Al2O3.

[0034] Comparative Example 2: Preparation of 1% Au / Al2O3

[0035] Take 0.1 mL of chloroauric acid aqueous solution, dissolve it in 150 mL of water, add alumina support, disperse it evenly, adjust the pH of the solution to 8 using sodium carbonate and maintain it for 2 h, filter, wash and dry, and calcine at 350 °C for 2 h in air atmosphere to obtain catalyst 1% Au / Al2O3.

[0036] The reaction evaluation of the catalysts in Comparative Examples 1-2 was conducted in a high-pressure reactor for the selective oxidation of ethylene glycol. 0.5 g of the catalyst prepared in Comparative Example 1 or Comparative Example 2, 0.01 g of sodium carbonate, and 10 mL of a methanol-ethylene glycol mixture (methanol / ethylene glycol molar ratio = 10:1) were used. The reactor was pressurized to 3 MPa, the reaction temperature was 120 °C, and the reaction time was 1 h. The ethylene glycol conversion and methyl glycolate selectivity results are shown in Table 1.

[0037] Table 1. Catalytic activity of catalysts in comparative examples 1-2 in the ethylene glycol oxidation reaction.

[0038]

[0039] Example 1: Preparation of oxide-supported palladium catalyst 1%Pd-1%Bi / Al2O3 by impregnation method

[0040] Catalyst preparation: 0.2 mL of a 20% bismuth nitrate aqueous solution was added dropwise to an alumina support, stirred until homogeneous, and allowed to stand at room temperature for 12 h. Then, it was dried at 120 °C for 2 h, and finally calcined at 600 °C in air for 3 h to obtain 1% Bi / Al₂O₃. Alternatively, 0.2 mL of a certain concentration of palladium chloropalladium acid aqueous solution was added dropwise to a Bi / Al₂O₃ support, ensuring a palladium to bismuth mass ratio of 1:1. The solution was allowed to stand at room temperature for 12 h, then dried at 120 °C for 2 h, calcined at 500 °C in air for 2 h, and finally reduced at 400 °C in hydrogen atmosphere for 2 h to obtain the catalyst 1% Pd-1% Bi / Al₂O₃.

[0041] Example 2:

[0042] Following the method in Example 1, a catalyst of 1% Pd-1% Zn / Al2O3 was obtained.

[0043] Example 3:

[0044] Following the method of Example 1, a catalyst of 1% Pd-1% Pb / Al2O3 was obtained.

[0045] Example 4:

[0046] Following the method of Example 1, a catalyst of 1% Pd-1% Co / Al2O3 was obtained.

[0047] Example 5:

[0048] Following the method in Example 1, a catalyst of 1% Pd-1% Ni / Al2O3 was obtained.

[0049] The reaction evaluation of the catalysts in Examples 1-5 was conducted in a high-pressure reactor for the selective oxidation of ethylene glycol. 0.5 g of catalyst, 0.01 g of sodium carbonate, and 10 mL of a mixed solution of ethylene glycol and methanol (methanol / ethylene glycol molar ratio = 10:1) were used. The reactor was pressurized to 3 MPa, the reaction temperature was 120 °C, and the reaction time was 1 h. The ethylene glycol conversion rate and methyl glycolate selectivity results are shown in Table 2.

[0050] Table 2. Activity of different catalysts prepared by impregnation method in the ethylene glycol oxidative esterification reaction.

[0051]

[0052] Compared with Comparative Example 1, the selectivity of methyl glycolate in Examples 1-5 was significantly improved, and comparable to the selectivity of the gold catalyst in Comparative Example 2.

[0053] Example 6: Preparation of palladium-based catalyst 1%Pd-1%Bi / Al2O3-D by deposition precipitation method

[0054] Catalyst preparation: 0.2 mL of a 20% bismuth nitrate aqueous solution was added dropwise to an alumina support, stirred until homogeneous, and allowed to stand at room temperature for 12 h. Then, it was dried at 120 °C for 2 h, and finally calcined at 600 °C in air for 3 h to obtain a bismuth-modified Al₂O₃ support. 0.2 mL of a chloropalladium acid aqueous solution was dissolved in 150 mL of water, and the bismuth-modified Al₂O₃ support was dispersed in the solution. The pH of the solution was adjusted to 10 using sodium carbonate at 60 °C and maintained for 4 h. Subsequently, the solution was filtered, washed, dried at 120 °C, calcined at 500 °C in air for 2 h, and finally reduced at 400 °C in hydrogen atmosphere for 2 h to obtain the catalyst 1%Pd-1%Bi / Al₂O₃-D.

[0055] Example 7

[0056] Following the method of Example 6, a catalyst of 1% Pd-1% Zn / Al2O3-D was obtained.

[0057] Example 8

[0058] Following the method of Example 6, the catalyst 1%Pd-1%Pb / Al2O3-D was obtained.

[0059] Example 9

[0060] Following the method of Example 6, the catalyst 1%Pd-1%Co / Al2O3-D was obtained.

[0061] Example 10

[0062] Following the method of Example 6, the catalyst 1%Pd-1%Ni / Al2O3-D was obtained.

[0063] The catalyst reaction evaluation in Examples 6-10 was conducted in a high-pressure reactor for the selective oxidation of ethylene glycol. 0.5 g of catalyst, 0.01 g of sodium carbonate, and 10 mL of a methanol-ethylene glycol mixture were used (methanol / ethylene glycol molar ratio = 10:1). The reactor was pressurized to 3 MPa, the reaction temperature was 120 °C, and the reaction time was 1 h. The ethylene glycol conversion and methyl glycolate selectivity results are shown in Table 3.

[0064] Table 3. Activities of different catalysts prepared by coprecipitation method in the ethylene glycol oxidative esterification reaction.

[0065]

[0066] Example 11: Preparation of catalyst 1%Pd-1%Bi / Al2O3-C by coprecipitation method

[0067] Catalyst preparation: 0.5 g of bismuth nitrate and 0.2 mL of 1 mol / L chloropalladic acid aqueous solution were dissolved in 150 mL of water. The Al2O3 support was dispersed in the above solution. The pH of the solution was adjusted to 11 using sodium carbonate at 70 °C and maintained for 4 h. Subsequently, the solution was filtered, washed, dried at 120 °C, calcined in air at 550 °C for 2 h, and finally reduced at 400 °C in hydrogen atmosphere for 2 h to obtain the catalyst 1%Pd-1%Bi / Al2O3-C.

[0068] Example 12

[0069] Following the method of Example 11, a catalyst of 1% Pd-1% Zn / Al2O3-C was obtained.

[0070] Example 13

[0071] Following the method of Example 11, a catalyst of 1%Pd-1%Pb / Al2O3-C was obtained.

[0072] Example 14

[0073] Following the method of Example 11, a catalyst of 1% Pd-1% Co / Al2O3-C was obtained.

[0074] Example 15

[0075] Following the method of Example 11, a catalyst of 1% Pd-1% Ni / Al2O3-C was obtained.

[0076] The catalyst reaction evaluation in Examples 11-15 was conducted in a high-pressure reactor for the selective oxidation of ethylene glycol. 0.5 g of catalyst, 0.01 g of sodium carbonate, and 10 mL of a methanol-ethylene glycol mixture were used (methanol / ethylene glycol molar ratio = 10:1). The reactor was pressurized to 3 MPa, the reaction temperature was 120 °C, and the reaction time was 1 h. The ethylene glycol conversion and methyl glycolate selectivity results are shown in Table 4.

[0077] Table 4. Activity of different catalysts prepared by deposition-precipitation method in the ethylene glycol oxidative esterification reaction.

[0078]

[0079] Example 16

[0080] A palladium-based catalyst supported on a composite oxide was prepared according to the preparation method of Example 11. The oxides Al2O3 and SiO2 were mixed at a mass ratio of 1:1 to replace the single Al2O3 support, and the catalyst 1%Pd-1%Bi / Al2O3-SiO2-D was prepared.

[0081] Example 17

[0082] Referring to the method of Example 16, by changing the type of metal supported and using different supports, a catalyst 1%Pd-1%Pb / MgO-SiO2-D was obtained.

[0083] Example 18

[0084] Referring to the method of Example 16, by changing the type of metal supported and using different supports, a catalyst 1%Pd-1%Co / Al2O3-MgO-D was obtained.

[0085] Example 19

[0086] Referring to the method of Example 16, by changing the type of metal supported and using different supports, a catalyst of 1%Pd-1%Ni / CaO-ZnO-D was obtained.

[0087] Example 20

[0088] Referring to the method of Example 16, by changing the type of metal supported and using different supports, a catalyst 1%Pd-1%Bi / SiO2-MgO-D was obtained.

[0089] The catalyst reaction evaluation in Examples 16-20 was conducted in a high-pressure reactor for the selective oxidation of ethylene glycol. 0.5 g of catalyst, 0.01 g of sodium carbonate, and 10 mL of a methanol-ethylene glycol mixture were used (methanol / ethylene glycol molar ratio = 10:1). The reactor was pressurized to 3 MPa, the reaction temperature was 150 °C, and the reaction time was 1 h. The ethylene glycol conversion and methyl glycolate selectivity results are shown in Table 5.

[0090] Table 5. Activity of catalysts supported on different composite oxides prepared by coprecipitation method in the ethylene glycol oxidative esterification reaction.

[0091]

Claims

1. A process for the catalytic oxidation esterification of ethylene glycol to methyl glycolate using a palladium-based nanolaminate catalyst, characterized in that, The method comprises the following steps: (1) impregnating a soluble salt of a modified metal on an oxide or composite oxide carrier, standing at room temperature for 10-24 h, drying, and then calcining at 400-700 ℃ in an air atmosphere to obtain a modified oxide or composite oxide carrier; then impregnating a palladium salt solution on the surface of the modified oxide or composite oxide carrier in an equal volume; or mixing the palladium salt aqueous solution with the modified oxide or composite oxide carrier, adding a lye to adjust the pH to 8-13, standing at room temperature for 2-24 h, drying, and then calcining at 400-700 ℃ in an air atmosphere, and finally reducing in a hydrogen atmosphere at 150-500 ℃ to obtain a catalyst; or directly impregnating a palladium salt solution and a soluble salt of a modified metal on an oxide or composite oxide, standing at room temperature for 10-24 h, drying, and then calcining at 400-700 ℃ in an air atmosphere, and finally reducing in a hydrogen atmosphere at 150-500 ℃ to obtain a catalyst; (2) loading the catalyst obtained in step (1) into a high-pressure reaction kettle, adding a mixed solution of an alkaline substance, ethylene glycol and methanol, and performing a reaction in an oxygen-containing atmosphere, wherein the reaction pressure is 0.5-5 MPa, and the reaction temperature is 80-200 ℃, and ethylene glycol is oxidized and esterified to obtain methyl glycolate; in step (1), the modified metal is one or a combination of two or more of bismuth, lead, cobalt, zinc and nickel, and the loading amount of the modified metal is 0.1-2 wt %; and the loading amount of palladium metal is 0.1-5 wt %; in step (1), the oxide is one of Al2O3, MgO, SiO2, CaO, ZnO, TiO2 and ZrO2, and the composite oxide is a mixture of two of Al2O3, MgO, SiO2, CaO, ZnO, TiO2 and ZrO2, and the mass ratio of the two oxides is 10:1-1:10; in step (2), the molar ratio of methanol to ethylene glycol is 0.1-50:1; and the addition amount of the catalyst is 0.1-20 wt % of the total amount of methanol and ethylene glycol.

2. The method of claim 1, wherein, in step (1), the loading amount of the modified metal is 0.5-1.5 wt %.

3. The method of claim 1, wherein, in step (1), the loading amount of palladium metal is 0.5-1.5 wt %.

4. The method of claim 1, wherein, in step (1), the palladium salt is one of a sulfate salt, a nitrate salt, an oxalate salt, a chloride salt, an acetate salt and a phosphate salt of palladium; and the soluble salt of the modified metal is one of a sulfate salt, a nitrate salt, an oxalate salt, a chloride salt, an acetate salt and a phosphate salt of the corresponding metal.

5. The method of claim 1, wherein, in step (1), the solute of the lye is one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonia water and urea.

6. The method of claim 1, wherein, in step (1), the drying is performed at 100-140 ℃, the calcination temperature is 400-600 ℃, the calcination time is 2-6 h, the reduction temperature is 300-500 ℃, and the reduction time is 1-5 h.

7. The method of claim 1, wherein, in step (2), the reaction pressure is 1-3 MPa, the reaction temperature is 100-130 ℃, and the reaction time is 0.5-24 h.

8. The method of claim 1, wherein, The basic substance in step (2) is sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and the concentration of the basic substance is 0.0001-0.1 g / mL.

9. The method of claim 1, wherein, The molar ratio of methanol and ethylene glycol in step (2) is 5-50:1; the amount of catalyst added is 1-10 wt% of the total amount of methanol and ethylene glycol.

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